Flexible PVC formulations comprising plasticizers, either petroleum-based or bio-based, and calcined clay filler have relatively poor insulation resistance. Blending of components typically results in compound performance close to the average of performance of the individual components.
U.S. Pat. No. 7,030,179 teaches the optimization of calcium carbonate (CaCO3) filler for a non-electrical PVC application.
U.S. Pat. No. 4,447,569 uses examples of a lead-containing composition on top of a fixed CaCO3/kaolin clay composition in PVC to demonstrate that addition of magnesium oxide (MgO) at 5.0 parts per hundred resin (phr) significantly improves the volume resistivity imparted by lead nonyl phenolate. It also teaches that while basic lead silicate sulfate complex (Controls C and D in the examples) show very high volume resistivity initially, the values fall off rather rapidly upon aging. Lead nonyl phenolate with epoxy (Examples 6 to 12) offer values which are only one-third as high at 50° C., but 81% of the values at 75° C.
U.S. Pat. No. 4,447,569 focuses on the uniqueness of lead alkyl phenolate in PVC electrical performance and includes sole CaCO3 and a blend of CaCO3/kaolin clay in the absence of lead alkyl phenolate as a control, but it offers no comparison with the sole use Kaolin clay as a filler.
There are environmental concerns for the use of lead-containing ingredients. Of current commercial interest are environmental friendly non-lead containing formulations that demonstrate enhanced electrical thermoplastic high heat-resistant nylon-coated (THHN) performance.